Method of making potassium ferricyanide



June f5 ,192"6.'

i G. BARsKY METHOD OF MAKING POTASSIUM FERRICYANIDE Filed Oct. z, 1925ATTORNEY Patented June 15, 1926. l

UNITED STATES PATENT` OFFICE..

GEORGE BARSKY, F NW YORK, N. Y., ASSIGNOR T0 AMERICAN CYANAMID COM-PANY, 0F NEW YORK, N. Y., A CORPORATION OF MAINE.

METHOD 0F MAKING '.PO'IASSIUM FERRICYANIDE.

Application led October 2, 1925. erial No. 60,046.

This invention relates to the production of tals which may be furtherpurified by repotassium ferricyanide by the oxidation of 'crystalhzatiomI do not carry the reaction ferrocyanide by chemical reagents. toabsolute completion but stop the intro- 55 It has been customary toVmake potassium duction of chlorine at a convenient point andferricyanide by providing a solution of pothus avoid the formation oftheundesirable tassium ferrocyanide and passing chlorine green compounds`incident to over-chlorinatherethiough, keeping the solution lcold tion.I have discovered that, contrary to throughout the operation untilconversion the' prior methods, it is not essential to keep 60 wascomplete. An excess of chlorine should the solution cool, but thatdecompositionl not be used, nor should the solution be alduring thereaction maybe prevented by the loWed to become Warm as such conditionsaddition of a small amount rof'a protective tend to the formation ofcomplex, insoluble, alkaline material, such as potassium hydrox-` greencompoundsA which are difficult to re- 1de, to the reacting mixture. Themother 65 move. The solution Was then evaporated liquor from' thecrystallized product, con- V l@ and the ferricyanide allowed tocrystallize on taining a number of constituents, is treated cooling; themother liquor was again evapto reduce the ferricyanide content ,toferroorated and the salt' crystallized therefrom, cyanide, and it thenreenters the process, and but it was contaminated with potassium I havefound thattliis reduction may be 70 chloride. This method Was fairlysuccessaccomplished in a very satisfactory manner ful but great care wasnecessaryto prevent by the use of calcium formate.

the solution from heating up and forming The accompanying drawing isaiowlsheet the undesirable green compounds, and the showingthe adaptationof my improvements introduction of chlorine into the solution to theproduction of potassium ferricyanide 7| had to be carefully regulated toconvert all from calcium feII'OCyanide.-

of the ferrocyanide Without adding an ex`4 I first prepare a solution lof calcium fercess thereof. The 'cost of evaporation of IOCyanide toWhich is added a sulicient the resulting solution was considerable.amount of potassium chloride 2 to form cal- The present invention isadapted to over- @111m potassium ferrocyanide 3, which pre?r 9 comethese difficulties, it being among the cipitates out and is removed by'4filtration. objects of this invention to provide a method Itis thendigested With potassium carbonate of making potassium ferricyanide inwhich 4= to produce potassium ferrocyanide solu- Y it shall not benecessary to maintain the solu- 131011 5 and Calcium Carbonate which isretion very cold during the reaction period, moved by filtration, andthe solution is eva u which shall avoid the necessity of evaporat-OI'eed Il 6 t0 Crystallize atleast part of t e 5 -ing the solution, andin which the control of fell'eyanide l into the resulting slurry,

the various factors entering into the reaction Which 00111381118 a Smalluantty lof potassium /ff//l/need not be veryclose. hydroxide, say 4% oft e ferrocyanide pres- It is also among the objects of my invenent toprevent decomposition, chlorine 7 isy .o

tion to provide a, substantially continuous passed causing oxidationofthe ferrocyanide i liquors are completely utilized inthe reacbut theDIOdlIGtOIl 0f Chlorine is Stopped tion. before all the ferroc anide' isconverted.

In practicing my invention I provide a, lCrystals of ferrie anidb areformed during` u solution of potassium ferrocyanideinto thegeaton Mld te Crystals 0f ferrocyanide process and one in which thevarious motherand 00I1VeIS0I1 t0 POSISSiUm ferl'cyallide 8 a which chlorine is passedas heretofore, but go Into' solution. The mixture is subjected I utilizea saturated solution containing an Y0 lfilOD, and the crystals areuried, excess of solid potassium ferrocyanide and, 1f desired, byrecrystallization in t e resas a result, as the reaction proceeds thepoence of a small amount .of potassium hy roxl o taium ferricyanide4roduced crystallizes v1de 9. The mother liquor 10 resulting from out ofthe solution Whi e the excess of potasthe recystallization of theferricyanide -is sium ferrocyanide is dissolved, giving subreturne tothe potassium ferrocyam'de sc lustantially lpure-potassium ferricyanidecrystion which is then sub1ected to the action of the chlorine, and itscontained potassium hydroxide furnishes the alkalinity necessary toprevent decomposition during the chlorination.

The mother liquor 11 from the filtration of the potassium ferricyanidecrystals contains potassium erricyanide and potassium chloride, istreated with calcium formate 12 and lime 13 in the presence of steam 14,resulting in the production of calcium potassium ferrocyanide 15together with other soluble and insoluble compounds, the Whole beingadded to the vessel in which calcium potassium ferrocyanide is beingprecipitated. The cycle of operations is then repeated.

In thepractice of my invention I need not start with calciumferrocyanide For instance, I-dissolved 9.3 kilograms of ground potassiumferrocyanide in 10 liters of water and added 200 grams of potassiumhydroxid`e,;the amount of potassium ferrocyanide present being in excessof its solubllity. The mixture was agit-ated and chlorine was passed inuntil the solution began to darken. Crystals of potassium ferricyanidewere formed and were filtered off and dried in a vacuum oven. Thefiltrate was boiled with 280 grams of calcium formate, (60% pure), and200 grams of lime, for two hours with -constant stirring. The mass wasfiltered and then digested with potassium carbonate, giving a solutionof potassium ferrocyanide which may be utilized for the production ofpotassium ferricyanide as above described, or for other purposes.

It will be noted that my process produces crystalline potassiumferricyanide directly 'Without the necessity of evaporating solutionsthereof with the consequent decomposition of ferricyanide which can onlybe avoided by evaporation in a vacuum, a relatively expensive rocedure.There is no substantial loss o cyanide in the process since the motherliquors producedare re-circulated in the system and I have obtained atotal recovery of materials of 98%, although the recovery offerricyanide at each operation is only to 75% of the total cyanidepresent. The proportions of ingredients used may be varied Within Widelimits with good results'and no close control of the details of theprocess is necessary as the addition of a small amount (2%-10%) ofpotassium hydroxide to the reaction mixture prevents ldecompositionwithout the necessity of artiicial' cooling of the solution other thanby use of ordinary cooling Water.l The product is relatively pure, eventhe first crude crystals containing less than 3% of potassium chlorideand about 0.8% of potassiumferrocyanide; a sim le recrystallization ofthe product reduces t e said impurities to `0.3% and 0.2%, respectively.Various changes may be made in the details of the process as will beunderstood by those skilled in the art, the

scope of my invention being defined in the -claims appended hereto.

ricyanide which comprises providing a solu-v tion of potassiumferrocyanide, adding a small amount of alkali thereto, oxidizing thesolution to ferricyanide by passing chlorine thereinto, ltering oi thecrystals formed and recovering the erroand ferricyanides from thefiltrate.

4. The method of making potassium ferricyanide which com rises providinga solution of potassium errocyanide, adding a small amount of alkalithereto, oxidizing the solution to ferricyanide by passing chlorinethereinto, filtering ol' the crystals formed and treating the filtrateto reduce the ferricyanide therein to errocyanide.

5. The method of making potassium ferricyanide which comprises providinga solution of potassium ferrocyanide, adding a small amount of alkalithereto, oxidizing the solution to ferricyanide by passing chlorinethere-into, filtering o the crystals formed and treating the ltrate toreduce the ferricyanide therein to ferrocyanide by adding an organicreducing agent thereto.

6. The method of making potassium ferricyanide which comprises providinga solution of potassium ferrocyanide, adding a small amount of alkalithereto, oxidizing the solution to ferricyanide by passing chlorine'thereinto, filtering off the crystalsv formed and )treating the filtrateto reduce the ferricyam'de therein to ferrocyanide by adding calciumformate thereto.

7. The method of making potassium ferricyanide which comprises providinga solution of potassium ferrocyanide,- adding a small amount of alkalithereto, oxidizing the solution to ferricyanide by passing chlorinethereinto, iiltering ol'.' the crystals formed and treating the filtrateto reduce the ferricyanide therein to ferrocyanide by adding calciumformate andlime thereto.

8./ The method of making potassium ferricyanide which comprisesproviding a solution of potassium ferrocyanide, adding a small amount'ofalkali thereto, oxidizing the solution to ferricyanide by passingchlorine thereinto,` filtering-off the crystals formed, treating thefiltrate to reduce the ferricyanide therein to ferrocyanide, and

converting the same to potassium ferrocyidizing the solution toferricyanide by passanide. in chlorine thereinto.

9. The method of making potassium fer- 1 n testimony whereof, I havehereunto 1Ql ricyanide which comprises providing a solusubscribed myname this 30th day of Sept., 5 tion of potassium ferrocyanide containingan 1925.

excess of solid potassium ferrocyanide, adding a small amount of alkalithereto and ox- GEORGE BARSKY.

